Exemplary passive entry systems for vehicles are described in U.S. Pat. No. 6,906,612 issued to Ghabra et al. and entitled “System and Method for Vehicle Passive Entry Having Inside/Outside Detection;” U.S. Pat. No. 7,446,648 issued to Ghabra and entitled “Passive Activation Vehicle System Alert;” U.S. Pat. No. 4,873,530 issued to Takeuchi et al. and entitled “Antenna Device In Automotive Keyless Entry System;” U.S. Pat. No. 4,942,393 issued to Waraksa et al. and entitled “Passive Keyless Entry System;” U.S. Pat. No. 5,499,022 issued to Boschini and entitled “Remote Control System For Locking And Unlocking Doors And Other Openings In A Passenger Space, In Particular In A Motor Vehicle;” U.S. Pat. No. 5,751,073 issued to Ross and entitled “Vehicle Passive Keyless Entry And Passive Engine Starting System;” U.S. Pat. No. 6,049,268 issued to Flick and entitled “Vehicle Remote Control System With Less Intrusive Audible Signals And Associated Methods;” and U.S. Pat. No. 6,236,333 issued to King and entitled “Passive Remote Keyless Entry System.”